Field of the Invention
The present invention relates to a planetary gear train of an automatic transmission for a vehicle. More particularly, the present invention relates to a planetary gear train of an automatic transmission for a vehicle which improves power delivery performance and fuel efficiency as a consequence of achieving nine forward speed stages using a minimum number of constituent elements, enlarging a span of gear ratios, and linearly increasing or decreasing step ratios between speed stages.
Description of Related Art
The recent increase in oil prices has caused car makers to meet global demands for improving fuel efficiency. As a result, research is being conducted on engines in terms of reducing weight and improving fuel efficiency by down-sizing, and research is also being conducted to ensure both drivability and competitiveness for maximizing fuel efficiency by implementing an automatic transmission with multiple speed stages.
However, in the automatic transmission, the number of internal components is increased as the number of gear shift stages is increased, and as a result, the automatic transmission may be difficult to mount, the manufacturing cost and weight may be increased, and power transmission efficiency may be deteriorated.
Accordingly, development of a planetary gear train which may bring about maximum efficiency with a small number of components is important in order to increase fuel efficiency enhancement effect through the multiple speed stages.
In this aspect, in recent years, automatic transmissions capable of achieving 8-speeds have been implemented and the research and development of a planetary gear train capable of implementing more speed stages has also been actively conducted.
Since a span of gear ratios of the recent 8-speed automatic transmission is merely 6.5 to 7.5, the 8-speed automatic transmission has no great effect of improving fuel efficiency.
In addition, since step ratios between speed stages may not be increased or decreased linearly in a case in which a span of gear ratios of the 8-speed automatic transmission is greater than or equal to 9.0, driving efficiency of an engine and drivability, of a vehicle may be deteriorated.
Accordingly, there is a need for development of a high efficient automatic transmission with 9 or more forward speed stages.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.